Chapter 18 Summary

As the Cavendish laboratory had recently developed a new kind of X-ray tube, Watson was able to take pictures twenty times faster and probe that TMV was helical in shape. Francis confirmed that Watson's picture did indeed show that TMV was a helix. There was nothing else of interest to him that Watson could learn from TMV, so he knew he must attack DNA directly.

A scientist named Chargaff had done experiments showing interesting relationships between the purine and pyrimidine bases in DNA. The number of adenine molecules in DNA was the same as the number of thymine molecules. Similarly, the number of guanine molecules was the same as the number of cytosine molecules. No one knew what this meant and there was some controversy about his data. However, Francis believed it was important. He worked to show that there was attraction between the bases that had...